A typical electric transfer switch (or circuit beaker) is used to switch electric loads from a normal main utility power supply to a standby emergency power supply when a power outage occurs caused by a variety of reasons, for example, earthquake, flooding, bombing, or other utility blackouts, and of course, it is used to switch electric loads from the standby emergency power supply back to the normal main utility power supply when the power outage is over.
In an electric transfer switch, one of the concerns is to control the transition time in switching from the main power supply to the standby emergency power supply. For example, it may be necessary to disconnect loads from both electric power supplies for a controllable time period to allow residual electricity to dissipate or discharge before being switched to the standby power source so that the transferred loads are appropriately switched over. Accordingly, the electric loads should be in a neutral position for a controllable period of time, whereby the electric loads do not contact either of the electric power supplies, e.g. the normal main utility power supply and the standby emergency power supply.
In addition, for a quick release/make operation, it may be necessary to store energy in a mechanism, e.g., a toggle mechanism, which can be used to open or close moveable contacts with respect to stationary contacts of an electric transfer switch. After connecting the moveable contacts to the stationary contacts, i.e., after moving the moveable contacts from a neutral open position to a closed position, it is required to lock the toggle mechanism in the closed position to maintain the contact between the moveable contacts and the stationary contacts. Further, in the closed position, when a "fault" current occurs, it is required not only to maintain the contact between the moveable contacts and the stationary contacts, but also lock the contacts in closed position so that the repulsive forces at contacts may not open the switch. Accordingly, it is desired to design an electric transfer switch having a toggle mechanism which solves these problems.
U.S. Pat. No. 5,004,875 discloses a stored energy contact operating mechanism for opening and closing primary contacts of a circuit breaker. However, the patent does not solve the above problems in an electric transfer switch.
U.S. Pat. No. 4,999,598 relates to a three-position actuating mechanism for an electric transfer switch for opening and closing moveable contacts with respect to contact blocks (stationary contacts) which are connected to various power sources, respectively. However, this type of three-position actuating mechanism does not lock the moveable contacts in a closed position so as to maintain contact between the moveable contacts and the stationary contacts. Further, a quick release/make contact of the electric transfer switch is not possible in this type of three-position actuating mechanism as disclosed in this patent.
The present invention provides an electric transfer switch having a three-position toggle mechanism, which solves these and many other problems associated with existing electric transfer switches.